Neutral pentacoordinate silicon fluorides derived from amidinate, guanidinate, and triazapentadienate ligands and base-induced disproportionation of Si2Cl6 to stable silylenes

Article abstract of DOI:10.1021/ic1020548

Pentacoordinate silicon fluorides L¹SiF₃ (2a), L ²SiF₃ (2b), and (L³SiF₂)₂ (2c)₂ based on amidinate (L¹ = PhC(N^tBu) ₂), guanidinate (L

Full text of DOI:10.1021/ic1020548

358 Inorg. Chem. 2011, 50, 358–364
DOI: 10.1021/ic1020548
Neutral Pentacoordinate Silicon Fluorides Derived from Amidinate, Guanidinate,
and Triazapentadienate Ligands and Base-Induced Disproportionation of Si2Cl6
to Stable Silylenes
†
†
†
‡
,†
€
Rajendra S. Ghadwal, Kevin Propper, Birger Dittrich, Peter G. Jones, and Herbert W. Roesky*
†
€
€
€
Institut fu€r Anorganische Chemie der Universitat Gottingen, Tammannstrasse 4, D 37077 Gottingen, Germany,
‡
€
and Institut fu€r Anorganische und Analytische Chemie der Technischen Universitat Braunschweig,
Hagenring 30, D 38106 Braunschweig, Germany
Received October 11, 2010
Pentacoordinate silicon fluorides L1SiF3 (2a), L2SiF3 (2b), and (L3SiF2)2 (2c)2 based on amidinate (L1 = PhC(NtBu)2),
guanidinate (L2 = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinate), and triazapentadienate (L3 = NC(NMe2)NC-
(NMe2)NAr; Ar = 2,6-iPr2C6H3) ligands were prepared by fluorination of the corresponding chlorosilanes L1SiCl3 (1a),
L2SiCl3 (1b), and L3SiCl2 (1c) with Me3SnF at ambient temperature. Compounds 1b, 1c, 2a, 2b, and (2c)2 were
characterized by 1H, 13C, 19F, and 29Si NMR spectroscopic studies. Molecular structures of 1b, 1c, 2a, and (2c)2 were
determined by single crystal X-ray structural analysis. Invariom refinement involving non-spherical scattering factors of
the Hansen-Coppens multipole model was performed for 1b. Compound L3SiF2 (2c) is dimeric both in the solid state
and in solution, whereas its chloro-analogue 1c is monomeric. The attempted synthesis of diamidinatotetrachlorodisilane
by reaction of lithium amidinate with Si2Cl6 led to the formation of the silane (1a) and the silylene L1SiCl (3). Reaction
of Si2Cl6 with N-heterocyclic carbenes (NHC) afforded NHC adducts of dichlorosilylene and SiCl4. A one pot method
for the preparation of base-stabilized silylenes from Si2Cl6 is discussed.
Introduction
by donor atoms (C, N, or P) have proved to be attractive
topics of research. Further progress in this field is driven by
the design and synthesis of new compounds with main group
elements.
Compounds with coordination numbers greater than four
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past few decades. Silicon(IV) halides are well-known as Lewis
acids, and compounds with hypervalent silicon were first
observed at the beginning of the 19th century.1 Compounds
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over, compounds with higher-coordinate silicon are known
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pubs.acs.org/IC
Published on Web 12/02/2010
2010 American Chemical Society

Article
Herein we report on the synthesis and characterization of
Inorganic Chemistry, Vol. 50, No. 1, 2011 359
using NHC or LiN(SiMe3)2 as a dehydrochlorinating agent.
As a continuation of these studies, we report herein a new
method for the preparation of base-stabilized silylenes
from Si2Cl6.
pentacoordinate silicon fluorides containing bidentate mono-
(amidinate, guanidinate) and bifunctional (triazapentadienate)
ligands by efficient fluorination of their chloro analogues
1a-1c with Me3SnF. The synthesis and characterization of
L2SiCl3 (1b) and L3SiCl2 (1c) are reported for the first time.
One pot methods for the synthesis of compounds with low
valent elements are undoubtedly important to obtain suffi-
cient amount of starting material for new reactions. Recently
we reported6d a nearly quantitative (79% yield) synthesis of
NHC-stabilized dichlorosilylenes by a clean one-step reac-
tion of NHC with HSiCl3. We further described6f the high-
yield synthesis of monochlorosilylene L1SiCl from L1SiHCl2
Experimental Section
General Procedures. All manipulations were carried out under
an inert atmosphere of nitrogen using standard Schlenk line tech-
niques or a glovebox. The solvents used were purified by MBRAUN
solvent purification system MB SPS-800. Compound 1c6a and
0
0
L3 Li (L3 = Me3SiNC(NMe2)NC(NMe2)NAr and Ar is
2,6-iPr2C6H3)11 were prepared according to literature methods.
All chemicals received from Aldrich were used without further
purification. C6D6 and THF-d8 were dried over Na metal and
distilled under nitrogen prior to use. 1H, 13C, 19F, and 29Si NMR
spectra were recorded using Bruker Avance DPX 200 or Bruker
Avance DRX 500 spectrometers. Elemental analyses were ob-
tained from the Analytical Laboratory of the Institute of Inor-
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Preparation of L2SiCl3 (1b). To 100 mL of a diethyl ether solu-
tion of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine
(L2H) (1.54 g, 11.06 mmol) was added a 2.5 M solution of tBuLi
(4.45 mL, 11.12 mmol) at -78 °C, and the mixture was stirred
for 4 h at room temperature. Into the resulting white suspension
SiCl4 (1.30 mL, 11.34 mmol) was syringed at -78 °C with con-
stant stirring. The reaction mixture was further stirred overnight.
The volatiles were removed under vacuum to obtain a white solid.
The solid was dissolved in toluene (50 mL) and filtered through
Celite. The resulting filtrate was reduced to 25 mL under vacuum
and stored at -35 °C in a freezer to yield compound 1b as colorless
crystals (2.71 g, 90%). Anal. Calcd (%) for C7H12Cl3N3Si (M =
272.63): C, 30.84; H, 4.44; N, 15.41. Found (%): C, 30.79; H, 4.34;
N, 15.29. 1H NMR (200 MHz, C6D6, 298 K): δ1.16 (m, 4H, CH2),
2.11 (t, J = 5.6 Hz, 4H, CH2), 2.93 (t, J = 5.6 Hz, 4H, CH2) ppm.
13C{1H} NMR (75 MHz, C6D6, 298 K): δ 22.53 (CH2), 37.54
(CH2), 44.04 (CH2), 154.62 (CN3) ppm. 29Si NMR (59 MHz,
C6D6, 298 K): δ -103.42 ppm.
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L3SiCl2 (1c). SiCl4 (0.82 mL, 7.12 mmol) was added to 100 mL
0
of a diethyl ether solution of L3 Li (2.82 g, 7.12 mmol) at -78 °C,
and then the reaction mixture was allowed to warm to room tem-
perature. After overnight stirring the LiCl formed was filtered off.
Removal of all volatiles from the filtrate resulted in a white solid.
Recrystallization from toluene (20 mL) afforded compound 1c as
colorless crystals (2.14 g, 72%). Anal. Calcd. for C18H29Cl2N5Si
(M = 414.45): C, 52.16; H, 7.05; N, 16.90. Found (%): C, 52.19; H,
7.08; N, 16.83. 1H NMR (200 MHz, C6D6, 298 K): δ 1.06 (d, J =
6.7 Hz, 6H, CHMe2), 1.30 (d, J = 6.7 Hz, 6H, CHMe2), 2.24
(s, 6H, NMe2), 2.94 (s, 3H, NMe2), 2.97 (s, 3H, NMe2), 3.27 (m,
2H, CHMe2), 6.98-7.05 (m, 3H, C6H3) ppm. 13C{1H} NMR
(75 MHz, C6D6, 298 K): δ 23.61 (CHMe2), 25.78 (CHMe2), 28.46
(CHMe2), 37.01, 37.07, 39.50 (NMe2), 125.10, 127.96, 137.42
(C6H3), 146.57 (ipso-C6H3), 161.66, 162.31 (NCN) ppm. 29Si
NMR (59 MHz, C6D6, 298 K): δ -30.57 ppm.
L1SiF3 (2a). THF (50 mL) was added to 1a (1.75 g, 4.87 mmol)
and Me3SnF (2.68 g, 16.66 mmol) in a Schlenk flask at room
temperature. Stirring of the reaction mixture for 20 min resulted in
the dissolution of Me3SnF and the formation of a colorless solu-
tion. After further stirring for 2 h, all volatiles were removed under
vacuum to obtain a white solid. Recrystallization from toluene
(20 mL) at -35 °C afforded 2a (1.13 g, 75%) as colorless crystals
after 20 h. Anal. Calcd (%) for C15H23F3N2Si (M = 316.44): C,
56.93; H, 7.33; N, 8.85. Found (%): C, 56.79; H, 7.30; N, 8.72. 1H
NMR (200 MHz, C6D6, 298 K): δ 1.05 (s, 18H, CMe3), 6.70-6.88
(m, 5H, C6H5) ppm. 13C{1H} NMR (125 MHz, THF-d8, 298 K): δ
31.44 (CMe3), 54.52 (CMe3), 128.31, 128.97, 129.11, 129.20,
(10) (a) Jones, C. Coord. Chem. Rev. 2010, 254, 1273–1289. (b) Power, P. P.
Nature 2010, 463, 171–177. (c) Haaf, M.; Schmedake, T. A.; West, R. Acc.
Chem. Res. 2000, 33, 704–714. (d) Mandal, S. K.; Roesky, H. W. Chem.
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Inorg. Chem. 2008, 47, 6692–6700.

360 Inorganic Chemistry, Vol. 50, No. 1, 2011
Ghadwal et al.
Table 1. Crystallographic Data and Structure Refinement for 1b and 1c
Table 2. Crystallographic Data and Structure Refinement for 2a and 2c
1b
1c
2a
(2c)2
formula
Fw
C7H12Cl3N3Si
272.64
C18H29Cl2N5Si
414.45
formula
Fw
C15H23F3N2Si
316.44
C36H58F4N10Si2
763.08
cryst size/mm
cryst syst
space group
T/°C
0.50 ꢀ 0.20 ꢀ 0.15 0.40 ꢀ 0.40 ꢀ 0.25
cryst size/mm
cryst syst
space group
T/°C
0.28 ꢀ 0.20 ꢀ 0.12 0.50 ꢀ 0.25 ꢀ 0.25
monoclinic
P21/c
triclinic
P1
triclinic
P1
monoclinic
C2
-173
-173
-173
-173
˚
˚
a/A
10.6177(3)
8.1230(2)
13.5089(4)
90
10.1387(4)
14.3972(6)
15.9813(6)
71.159(4)
75.077(4)
85.845(4)
2133.18(15)
1.290
a/A
8.7620(9)
8.9751(9)
10.9816(12)
93.738(9)
100.701(9)
107.182(9)
804.05(15)
1.307
14.4012(3)
14.4485(3)
9.8332(2)
90
˚
b/A
˚
c/A
˚
b/A
˚
c/A
R/deg
β/deg
γ/deg
R/deg
β/deg
γ/deg
101.155(1)
90
101.970(1)
90
3
3
˚
˚
V/A
1143.10(5)
1.584
V/A
2001.56(7)
1.270
Dcalcd/g cm-3
Dcalcd/g cm-3
Z
wavelength/ A
4
4
Z
wavelength/A
2
2
˚
˚
1.54184
7.994
0.71073
0.37
0.71073
0.17
1.54184
1.29
abs coeff/mm-1
abs coeff/mm-1
θ range/deg
reflns collected/indep reflns
4.87 to 72.35 3.36 to 30.03
24058/2370 73335/11924
[R(int) = 0.0418] [R(int) = 0.0255]
θ range/deg
reflns collected/indep reflns
2.79 to 30.99 4.38 to 72.93
23331/5091 21748/3915
[R(int) = 0.0308] [R(int) = 0.0276]
max. and min transmn
final R1 indices
wR2 indices (all data)
0.380 and 0.109
0.0234
0.0243
1.000 and 0.949
0.0296
0.0839
max. and min transmn
final R1 indices [I > 2σ(I)]
wR2 indices (all data)
0.999 and 0.946
0.0311
0.0876
0.4701and 0.3717
0.0242
0.0246
3
3
˚
˚
largest diff peak and hole/e A 0.61 and -0.46
0.51 and -0.24
largest diff peak and hole/e A 0.38 and -0.20
0.21 and -0.15
equipped with a SMART 6000 CCD detector and a Cu KR
rotating anode. Integration was performed with SAINT.13 For
absorption and scaling of intensity data the SADABS pro-
gram14 was used. Structures were solved using direct methods and
refined by full-matrix least-squares against F2 with SHELXL-97.12
Non-hydrogen atoms were refined anisotropically. For hydro-
gen, positions and isotropic displacement parameters were re-
fined. The asymmetric unit of 2c contains half a molecule. For
compound 1b, the Independent Atom Model (IAM) refinement
starting values were used for Invariom refinement15 which is
based on the Hansen and Coppens multipole formalism.16 This
non-spherical atom refinement, which included reflections with
[F > 3σ (F)], was performed with XDLSM as part of the XD
package.17 XD input files were processed with the program
InvariomTool.18 In the Invariom refinement multipole param-
eters are fixed at theoretically predicted values, and only the
positional and displacement parameters are refined, providing a
more accurate structural model. Full details of the general
Invariom modeling procedure can be found in literature.18
131.24, 132.62 (C6H5), 177.11 (C6H5C) ppm. 19F NMR (188 MHz,
C6D6, 298 K): δ -132.38 (JSi-F = 219.3 Hz) ppm. 29Si NMR
(99 MHz, C6D6, 298 K): δ -124.91(quartet, JSi-F = 219.3 Hz)
ppm.
L2SiF3 (2b). Tetrahydrofuran (THF, 50 mL) was added to a
mixture of 1b (1.57 g, 5.76 mmol) and Me3SnF at room tem-
perature. After 5 min the Me3SnF had dissolved, resulting in a
colorless solution. The volatiles were removed under vacuum to
obtain a white solid. Recrystallization from toluene at -35 °C
afforded colorless crystals of 2b (1.01 g, 79%). Anal. Calcd (%)
for C7H12F3N3Si (M = 223.27): C, 37.66; H, 5.42; N, 18.82.
1
Found (%): C, 37.59; H, 5.33; N, 18.64. H NMR (200 MHz,
C6D6, 298 K): δ 1.26 (m, 4H, CH2), 2.31 (t, J = 6.0 Hz, 4H,
CH2), 2.83 (t, J = 6.0 Hz, 4H, CH2) ppm. 13C{1H} NMR
(125 MHz, C6D6, 298 K): δ 23.23 (CH2), 39.56 (CH2), 43.34
(CH2), 155.32 (CN3) ppm. 19F NMR (188 MHz, C6D6, 298 K):
δ -137.76 (JSi-F = 203.7 Hz) ppm. 29Si NMR (59 MHz, C6D6,
298 K): δ -127.96 (quartet, JSi-F = 203.7 Hz) ppm.
L3SiF2 (2c). Compound 2c was prepared analogously to 2b,
using 1c (1.54 g, 3.72 mmol) and Me3SnF (1.37 g, 7.49 mmol), as
colorless crystals (1.11 g, 78%). Anal. Calcd. for C18H29F2N5Si
(M = 381.54): C, 56.66; H, 7.66; N, 18.36. Found (%): C, 56.67;
Results and Discussion
Synthesis and Characterization. The reaction of L1SiCl3
(1a) with Me3SnF in THF at room temperature led to the
immediate dissolution of Me3SnF with the formation of
L1SiF3 (2a) with pentacoordinate silicon atom. (Scheme 1).
Deprotonation of 1,3,4,6,7,8-hexahydro-2H-pyrimido-
1
H, 7.55; N, 18.23. H NMR (200 MHz, C6D6, 298 K): δ 1.14
(d, J = 6.7 Hz, 6H, CHMe2), 1.23 (d, J = 6.6 Hz, 6H, CHMe2),
2.40 (s, 6H, NMe2), 2.62 (s, 3H, NMe2), 2.81 (s, 3H, NMe2), 3.43
(m, 2H, CHMe2), 7.00-7.09 (m, 3H, C6H3) ppm. 13C{1H}
NMR (125 MHz, C6D6, 298 K): δ 24.31 (CHMe2), 25.56
(CHMe2), 29.32 (CHMe2), 37.23, 37.66, 40.31 (NMe2), 126.12,
128.00, 137.55 (C6H3), 147.07 (ipso-C6H3), 162.46, 162.81
(NCN) ppm. 19F NMR (188 MHz, C6D6, 298 K): δ -135.54
(JSi-F = 206.6 Hz) ppm. 29Si NMR (99 MHz, C6D6, 298 K):
δ -132.03 (t, JSi-F = 206.6 Hz) ppm.
t
[1,2-a]pyrimidine (L2H) with BuLi and subsequent treat-
ment with SiCl4 gave compound 1b, which reacts with
Me3SnF in THF 0to afford 2b (Scheme 2).
0
Reaction of L3 Li (where L3 = Me3SiNC(NMe2)NC-
(NMe2)NAr and Ar = 2,6-iPr2C6H3) with SiCl4 yielded
Single Crystal X-ray Structure Determinations. Crystal data
are summarized in Tables 1 and 2. Data for 1c and 2a were re-
corded on an Oxford Diffraction Xcalibur diffractometer using
monochromated Mo KR radiation. Empirical multiscan absorp-
tion corrections were performed. Structural parameters were
refined anisotropically on F2 using the program SHELXL-97.12
Hydrogen atoms were included using a riding model or rigid
methyl groups. A crystal of each of the compounds 1b
and 2c was mounted on a Bruker three circle diffractometer
(13) APEX2, SAINT, and SHELXTL; Bruker AXS Inc.: Madison, WI,
2009.
€
€
(14) Sheldrick, G. M. SADABS; University of Gottingen: Gottingen,
Germany, 2009.
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(15) Dittrich, B.; Hubschle, C. B.; Messerschmidt, M.; Kalinowski, R.;
Girnt, D.; Luger, P. Acta Crystallogr. 2005, A 61, 314–320.
(16) Hansen, N. K.; Coppens, P. Acta Crystallogr. 1978, A 34, 909–921.
ꢀ
(17) Koritsanszky, T.; Richter, T.; Macchi, P.; Volkov, A.; Gatti, C.;
Howard, S.; Mallinson, P. R.; Farrugia, L.; Su, Z. W.; Hansen, N. K. XD,
€
XDLSM; Freie Universitat Berlin: Berlin, Germany, 2003.
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(18) Hubschle, C. B.; Luger, P.; Dittrich, B. J. Appl. Crystallogr. 2007, 40,
623–627.
(12) Sheldrick, G. M. Acta Crystallogr. 2008, A 64, 112–122.

Article
Inorganic Chemistry, Vol. 50, No. 1, 2011 361
compound 1c with the elimination of LiCl and Me3SiCl.
3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene 4a or
IMes =1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene
In contrast to transition metal11 complexes, where the
0
triazapentadienate ligand (L3 )- is monoanionic, L3 in 1c
is dianionic (L3)2- because of the elimination of Me3SiCl
group. Treatment of 1c with Me3SnF affords compound
2c (Scheme 3).
4b)6d and NHC SiCl4 (NHC = IPr 5a or IMes 5b)6c,d
instead of (NHC SiCl3)2. The physical properties and NMR
3
3
spectral data of these compounds 1a, 3, 4a, 4b, 5a, 5b are
identical with those reported in literature.6a,c,d Thermal19
and base-induced20 disproportionation of Si2Cl6 to SiCl2
and SiCl4 is known, and trapping experiments of SiCl2 with
unsaturated substrates have been reported in the litera-
ture,21 but no stable silylenes have been isolated using this
method. Therefore, careful selection of the ligands and their
treatment with Si2Cl6 may serve as an indicator of silylene
stability for a given ligand. Further investigations in this
direction are continuing, and the results will be published in
due course.
Base-Induced Disproportionation of Si2Cl6 to Stable
Silylenes. Reaction of Si2Cl6 with lithium amidinate (L1Li)
resulted in the formation of trichlorosilane (1a) and mono-
chlorosilylene (L1SiCl) (3)6a (Scheme 4) instead of the
expected diamidinatotetrachlorodisilane (L1SiCl2SiCl2L1).
This finding offers a new one pot method for the prepara-
tion of base-stabilized silylenes. Similarly, reaction of Si2Cl6
with 2 equiv of NHC afforded NHC SiCl2 (NHC is IPr = 1,
3
Scheme 1
Compounds 1b, 1c, 2a, 2b, and 2c are colorless crystal-
line solids, soluble in common organic solvents, and are
stable under an inert atmosphere. These compounds were
characterized by elemental analyses, 1H, 13C, 19F, and 29Si
NMR spectroscopic studies. Compound 2a shows 1H and
13C NMR resonances for the amidinato moiety. 1H and
13C NMR spectra of 1b and 2b exhibit resonances for the
cyclic guanidinate ligand coordinated to the silicon atom
in a bidentate fashion. The conversion of monofunctional
triazapentadienate to bifunctional ligand in the forma-
1
tion of compound 1c can be clearly seen in the H and
13C NMR spectra. The resonance from the Me3Si group is
absent, and the methyl groups of the NMe2 substituents
appear as three sets of resonances in the 1H and 13C NMR
spectra. In the 1H NMR spectrum of 1c, one resonance at
δ 2.40 (s, 6H, Me2NCdN) ppm is preliminarily assigned
to the NMe2 group attached to the carbon atom of the
CdN-Si moiety, whereas the two resonances at δ 2.62
(s, 3H, Me2N) and 2.81 (s, 3H, Me2N) ppm are assigned to
the NMe2 group at the carbon atom of the C-N-Si
moiety. The presence of a bulky 2,6-iPr2C6H3 group at the
adjacent amine nitrogen restricts the free rotation of the
NMe2 group with the consequence that at room tempera-
ture two singlets appear. Compounds 2a-2c show the
expected resonances in the 1H and 13C NMR spectra. 2a,
2b, and 2c exhibit 19F NMR resonances at δ -132.38,
Scheme 2
Scheme 3

362 Inorganic Chemistry, Vol. 50, No. 1, 2011
Ghadwal et al.
Scheme 4
-137.76, -135.54 ppm, respectively, with JSi-F ranging
from 203 to 219 Hz. Compounds 1b, 2a, and 2b each show
a sharp 29Si NMR resonance in the range δ -103.42 to
-127.96 ppm, consistent for pentacoordinate6 silicon.
The presence of tetracoordinate silicon in 1c, in which
triazapentadienate is a bifunctional ligand, is further sup-
ported by a sharp 29Si NMR resonance at δ -30.57 ppm.
The appearance of the 29Si NMR resonance at δ -132.03
ppm for 2c indicates the retention of pentacoordinate
silicon in solution. Single crystal X-ray structural anal-
ysis shows the dimeric nature of 2c with pentacoordinate
silicon.
are summarized in Tables 1 and 2. The molecular struc-
ture of complex 1b, which crystallizes in the monoclinic
space group C2/c, is shown in Figure 1. The silicon
atom in 1b is pentacoordinate, and the bond angles
around silicon indicate a distorted trigonal-bipyramidal
geometry, whereby N(2) and Cl(1) occupy axial and
N(1), Cl(2), Cl(3) equatorial positions. The main dis-
tortion is imposed within the four-membered ring by
the small bite angle (71.60(4)°) of the bicyclic guanidi-
nate (L2) ligand.22 The C(1)-N(1) (1.3570(12) (A)) and
˚
˚
C(1)-N(2) (1.3280(14) (A)) bond distances are indicative
of π-delocalization from the amide nitrogen. As expected,
the equatorial Si(1)-Cl(2) and Si(1)-Cl(3) bonds are
noticeably shorter than the axial Si(1)-Cl(1) bond. A
similar trend can be seen in the Si-N bond distances
Single Crystal X-ray Structures. Molecular structures
of compounds 1b, 1c, 2a, and 2c were determined by
single crystal X-ray crystallography and are shown in
Figures 1-4. Crystallographic data for 1b, 1c, 2a, and 2c
˚
Si(1)-N(1) 1.7831(10) and Si(1)-N(2) 1.8684(8) A.
Complex 1c crystallizes in the triclinic space group P1
with two independent molecules, which are however closely
(19) (a) Goldberg, N.; Ogden, J. S.; Almond, M. J.; Walsh, R.; Cannady,
J. P.; Becerra, R.; Lee, J. A. Phys. Chem. Chem. Phys. 2003, 5, 5371–5377.
(b) Heinicke, J.; Vorwerk, D.; Zimmermann, V. J. Anal. Appl. Pyrolysis 1994, 28,
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related (rms deviation 0.20 A). It features a distorted
(22) (a) Kummer, D.; Halim, S. H. A.; Kuhs, W.; Mattern, G. J. Organomet.
Chem. 1993, 446, 51–65. (b) Coles, M. P.; Hitchcock, P. B. Dalton Trans. 2001,
1169–1171. (c) Coles, M. P.;Hitchcock, P. B. Organometallics 2003, 22, 5201–5211.
(d) Oakley, S. H.; Coles, M. P.; Hitchcock, P. B. Dalton Trans. 2004, 1113–1114.
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(f) Soria, D. B.; Grundy, J.; Coles, M. P.; Hitchcock, P. B. J. Organomet. Chem.
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Article
Inorganic Chemistry, Vol. 50, No. 1, 2011 363
Figure 1. Molecular structure of 1b. Anisotropic displacement param-
eters are depicted at the 50% probability level. H atoms are omitted for
clarity. Selected bond distances (A) and angles (deg): Si(1)-N(1)
1.7831(10), Si(1)-N(2) 1.8684(8), Si(1)-Cl(1) 2.1669(3), Si(1)-Cl(2)
2.0778(3), Si(1)-Cl(3) 2.0900(3), N(2)-C(1) 1.3280(14), N(1)-C(1)
1.3570(12), N(3)-C(1) 1.3144(13); N(1)-Si(1)-N(2) 71.60(4), N(1)-
Si(1)-Cl(2) 117.37(3), N(2)-Si(1)-Cl(2) 97.73(3), N(1)-Si(1)-Cl(3)
133.49(3), N(2)-Si(1)-Cl(3) 93.18(3), Cl(2)-Si(1)-Cl(3) 107.924(15),
N(1)-Si(1)-Cl(1) 91.56(3), N(2)-Si(1)-Cl(1) 161.67(3), Cl(2)-Si(1)-
Cl(1) 96.472(12).
Figure 3. Molecular structure of 2a. Anisotropic displacement param-
eters are depicted at the 50% probability level. H atoms are omitted for
clarity. Selectedbond distances(A) and angles (deg): Si(1)-F(1) 1.6214(6),
Si(1)-F(2) 1.5988(6), Si(1)-F(3) 1.5947(7), Si(1)-N(1) 1.9120 (8), Si(1)-
N(2) 1.8026 (8); F(2)-Si(1)-F(1) 94.34(3), F(3)-Si(1)-N(2) 120.70(4),
F(3)-Si(1)-N(1) 92.57(3), F(1)-Si(1)-N(1) 167.31(3), N(2)-Si(1)-
N(1) 70.25(3).
˚
˚
Figure 4. Molecular structure of (2c)2. Anisotropic displacement param-
eters are depicted at the 50% probability level. H atoms are omitted for
clarity. Primes indicate symmetry-generated atoms. Selected bond dis-
Figure 2. Molecular structure of 1c. Anisotropic displacement param-
eters are depicted at the 50% probability level. H atoms are omitted for
˚
tances (A) and angles (deg): Si-F(1) 1.6401(7), Si-F(2) 1.6218(8), Si-
N(1) 1.7685(10), Si-N(1)0 1.8138(9); F(2)-Si-F(1) 93.27(4), F(2)-
Si-N(1) 119.41(5), F(1)-Si-N(1) 93.83(4), F(1)-Si-N(1)0 170.20(4),
Si-N(1)-Si0 101.28(4), N(1)-Si0-N(3) 91.24(4).
˚
clarity. Selected bond distances (A) and angles (deg) (second values
refer to the second independent molecule): Si(1)-N(3) 1.6501(10),
1.6479(10), Si(1)-N(1) 1.7494(9), 1.7487(9), Si(1)-Cl(1) 2.0568(4),
2.0533(4), Si(1)-Cl(2) 2.0361(4), 2.0362(4), N(1)-C(1) 1.4023 (14),
1.4019(14), N(2)-C(1) 1.3113 (14), 1.3120(14), N(2)-C(2) 1.3824 (15),
1.3810(14), N(3)-C(2) 1.3172 (15), 1.3417(15); N(3)-Si(1)-N(1)
108.12(5), 108.70(5), N(3)-Si(1)-Cl(2) 113.72(4), 113.31(4), N(1)-
Si(1)-Cl(2) 108.31(3), 108.46(3), N(3)-Si(1)-Cl(1) 111.12(4), 110.05(4),
N(1)-Si(1)-Cl(1) 110.56(3), 112.07(3), Cl(2)-Si(1)-Cl(1) 104.962(18),
104.254(19).
consistent with known values of compounds with tetra-
coordinate silicon.23
Compound 2a crystallizes in the triclinic space group
P1 with distorted trigonal bipyramidal geometry around
the pentacoordinate silicon atom (Figure 3). The atoms
N(1) and F(1) occupy the axial positions, whereas N(2),
F(2), and F(3) are equatorial. Analogously to compound
1b, the differently disposed nitrogen atoms of the biden-
tate amidinate (L1) ligand cause the main distortion, with
a N(1)-Si(1)-N(2) bond angle of 70.25(3)°, and the axial
tetrahedral geometry at the tetracoordinate silicon (Figure 2).
The NCNCN moiety shows, beginning at N(3), a short-
long-short-long pattern of C-N bond distances. The
˚
Si(1)-N(3) bond (1.6501(10), 1.6479(10) A in the two
molecules) is significantly shorter than Si(1)-N(1) (1.7494(9),
1.7487(9) A), associated with the presence of the bulky
˚
Si(1)-F(1) bond (1.6214(6) A) is slightly longer than its
˚
equatorial counterparts (av 1.5967(7) A).2s Similarly, the
˚
2,6-iPr2C6H3 group on N(1) compared to the unsubsti-
˚
Si-N bond distances are 1.8026(8) and 1.9120(8) A respec-
˚
tuted N(3). The Si-Cl bond distances (av 2.046 A) are
tively for the axial and equatorial Si-N bonds. The C(1)-
˚
˚
N(1) (1.3135(11)A and C(1) -N(2) (1.3641(10) A) bond
lengths are indicative of π-delocalization through the
amide nitrogen.
(23) Ghadwal, R. S.; Roesky, H. W.; Merkel, S.; Stalke, D. Chem.;Eur.
J. 2010, 16, 85–88.

364 Inorganic Chemistry, Vol. 50, No. 1, 2011
Ghadwal et al.
The molecular structure of compound 2c is shown in
Figure 4. 2c crystallizes in the monoclinic space group C2
as a dimer with imposed 2-fold symmetry. The dimeric
nature of 2c also persists in solution at room temperature.
The 29Si NMR spectrum of 2c displays a triplet at
δ -132.03 ppm consistent with a pentacoordinate silicon
atom. Clearly the monomeric molecules of L3SiF2 (2c)
react in a [2 þ 2] cycloaddition at the Si-N bonds to yield
dimeric (L3SiF2)2 (2c)2. Each of the silicon atoms features
distorted trigonal-bipyramidal geometry. The nitrogen
atoms of ligand L3 occupy one axial and one equatorial
position at the same silicon atom. The second axial posi-
tion is filled by one fluorine atom, and the remaining equa-
torial positions are occupied by the second fluorine atom
and symmetry-generated nitrogen. The usual pattern of
bond lengths is observed.
Conclusion
A direct fluorination method for the preparation of fluo-
rides with pentacoordinate silicon based on amidinate, gua-
nidinate, and triazapentadienate ligands is reported. A one
pot method is discussed for the generation of stable silylenes
from base-induced disproportionation of Si2Cl6. This method
may serve as a key reaction for generating silylenes and trap-
ping the silylene intermediates with various bases. Invariom
refinement involving non-spherical scattering factors of the
Hansen-Coppens multipole model was performed for 1b.
Acknowledgment. Financial support from the Deutsche
Forschungsgemeinschaft is gratefully acknowledged.
Supporting Information Available: Crystallographic data for
complexes 1b, 1c, 2a, and 2c as CIF files. This material is avail-
able free of charge via the Internet at http://pubs.acs.org.